1. Field of the Invention
The present invention relates to a canceling structure of a combination switch, such as a turn signal switch for activating, for example, a turn signal lamp of a vehicle.
2. Description of Related Art
As such a canceling structure, there is a canceling structure of a turn signal switch as previously proposed by the inventor in JP-A-2001-10406. A turn signal switch incorporating this canceling structure is shown in FIGS. 4 and 5.
In this case, a swing block 2 having a control lever 1 is rotatably supported by a casing 3 and a cover 6 around a shaft 2a, and a cancel cam 9 is disposed between the swing block 2 and the cover 6. Referring to FIG. 5, the control lever 1 can be rotated vertically in the direction shown by arrows C and D around a lever shaft Q relative to the swing block 2; however, referring to FIG. 4, the control lever 1 is rotated horizontally in the direction shown by arrows A and B along with the swing block 2 around the shaft 2a to move in the direction corresponding to the rotation of a steering shaft 14.
The swing block 2 includes an arm 2k for pushing a moderate body 8 at the end thereof biased by a moderate spring 7 against a moderate groove 3b formed in the casing 3.
An upper shaft 9b of the cancel cam 9 can be moved along a long hole 6b formed in the cover 6 in a normal mode. As particularly shown in an enlarged view of FIG. 6, the cancel cam 9 is biased longitudinally toward a steering shaft 14 by a coil spring 11 via an elastic contact material 12. In the drawing, reference numeral 6d denotes a guide formed at the lower surface of the cover 6 and guides the elastic contact material 12 on the line connecting the steering shaft 14 with the shaft 2a of the swing block 2.
Returning to FIGS. 4 and 5, the swing block 2 is provided with a support groove 2c for receiving a lower shaft 9a coaxial with the upper shaft 9b of the cancel cam 9. The support groove 2c includes an angular projection 2d at the center thereof in the direction from the steering shaft 14 toward the shaft 2a of the swing block 2. When the control lever 1 is in a neutral position, the lower shaft 9a of the cancel cam 9 is positioned at the top of the angular projection 2d and a butting portion 9c is positioned out of a rotating path of the cancel pin 10.
As shown in FIG. 6, the cancel cam 9 includes a pressure contact surface 9e in contact with the upper shaft 9b and coming into contact with a pushing face 12a of the elastic contact material 12, the butting portion 9c extending toward the steering shaft 14, and a pressure portion 9d extending toward the shaft 2a for pushing against a cam guide 13, which will be described later. FIG. 7 is an enlarged perspective view showing the cancel cam 9, the elastic contact material 12, and the coil spring 11.
The cam guide 13 is formed in substantially U shape in FIG. 4, which is slidably placed on the swing block 2 only along the shaft 2a of the swing block 2, is pushed by a pressure spring 15 to be biased toward the cancel cam 9, movement of projections 13a formed on right and left sides thereof toward the steering shaft 14 is limited by a support 2h, and the inner wall in the U-shape is separated from the pressure portion 9d of the cancel cam.
When the control lever 1 is operated toward a leftward indicating position shown by arrow A to rotate the swing block 2 integrated with the control lever 1 around the shaft 2a, the angular projection 2d of the support groove 2c is moved and the cancel cam 9 is pushed by the elastic contact material 12 biased by the coil spring 11, and the lower shaft 9a slides down the slope of the angular projection 2d to move to the base of the angular projection 2d and the upper shaft 9b is moved toward the steering shaft 14 along the long hole 6b in the cover 6. Consequently, the butting portion 9c of the cancel cam 9 projects into the rotating path of the cancel pin 10 which rotates along with the steering shaft 14.
The cam guide 13 is rotated around the shaft 2a along with the swing block 2. As a result, the sidewall of the cam guide 13, on the upper side in FIG. 4, is positioned in contact with the side end of the pressure portion 9d of the cancel cam 9. The swing block 2 slides a moving part having a moving contact for a turn signal lamp, and thus, the moving contact is brought into contact with a fixed contact to blink a left turn signal lamp.
In this state, when a steering handle is operated in the same direction as the control lever 1 to rotate the steering shaft 14 leftward in the direction shown by arrow J, the cancel pin 10 pushes the butting portion 9c in the direction shown by arrow E to rotate the cancel cam 9 around the lower shaft 9a and the upper shaft 9b. 
During the rotation, the pressure portion 9d of the cancel cam is only separated from the sidewall of the cam guide 13 that was close thereto, not obstructing the rotation.
By the rotation, the pressure contact surface 9e of the cancel cam 9 is rotated to compress the coil spring 11 via the elastic contact material 12; however, since a contact point between the pressure contact surface 9e and the elastic contact material 12 is separated from the lower shaft 9a and the upper shaft 9b, the cancel cam 9 is subjected to a rotating force by the coil spring 11, thereby returning to an initial state after the cancel pin 10 has been separated from the butting portion 9c. 
During this period of time, since the swing block 2 pushes the moderate body 8 at the end of the arm against the cam groove 3b, the control lever 1 is held in the leftward indicating position rotated in the direction shown by arrow A.
Next, in this leftward indicating position, when the steering handle is operated to rotate the steering shaft 14 rightward in the direction shown by arrow K, the cancel pin 10 pushes the butting portion 9c in the direction shown by arrow F to rotate the cancel cam 9 around the lower shaft 9a and the upper shaft 9b. 
By this rotation, the pressure portion 9d of the cancel cam pushes at the sidewall of the cam guide 13 which was close thereto. Accordingly, the swing block 2 having the cam guide 13 is rotated in the direction shown by arrow B to return to the neutral position, and the control lever 1 also returns to OFF position automatically, thereby turning off the left turn signal lamp.
With the return of the swing block 2, the angular projection 2d of the support groove 2c biases the lower shaft 9a to move the cancel cam 9 in the direction apart from the steering shaft 14, thus separating the butting portion 9c from the rotating path of the cancel pin 10.
The same goes for a case in which the control lever 1 is operated in the direction shown by arrow B, except that the direction of operation is reversed.
When the control lever 1 is rotated leftward in the direction shown by arrow A, and with the position held by hand, the steering handle is rotated rightward in the direction of returning the control lever 1 automatically, the cancel cam 9 which is forced to rotate by the pressure of the cancel pin 10 rotating in the direction shown by arrow K rotates in the direction shown by arrow F to push the pressure portion 9d against the sidewall of the cam guide 13. In this case, since the sidewall of the cam guide 13 is inclined, the cam guide 13 is moved toward the shaft 2a against the pressure spring 15, the rotation of the cancel pin 10 and the cancel cam 9 is allowed, thus causing no damage by the application of an excessive force.
When the cancel pin 10 is further rotated and passes through the cancel cam 9, the cam guide 13 returns to a position before the cancel cam 9 abuts thereon by the elasticity of the pressure spring 15, and the cancel pin 10 returns there by the elasticity of the coil spring 11.
The same goes for the case in which the control lever 1 is operated inversely and held therein.
The other structures including the connecting structure of the control lever 1 to the swing block 2 and the operation thereof are specifically described in JP-A-2001-10406.
With such a structure, when the control lever 1 is operated to rotate the steering handle in a desired rotating direction, and then the steering handle is returned, the control lever 1 returns automatically to the neutral position.
The coil spring 11 for returning the cancel cam 9 onto a line connecting the steering shaft 14 and the shaft 2a of the swing block is arranged to be aligned with the line, thus having the advantage of reducing the occupied area of the returning structure and also the width of the casing.
In the canceling structure of the turn signal switch described above, the pressure contact surface 9e of the cancel cam 9 is formed as a plane in contact with the upper shaft 9b, and similarly, the pressure surface 12a of the elastic contact material 12 in contact with the pressure contact surface 9e is shaped in plane. However, after the butting portion 9c of the cancel cam 9 has been pushed by the cancel pin 10 rotating in the same direction as the control lever to rotate around the upper shaft 9b (and the lower shaft 9a), sometimes the cancel cam 9 cannot return smoothly.
The following may be a cause after the consideration of the above problems.
When the cancel cam 9 is rotated, the coil spring 11 is compressed to displace the elastic contact material 12 and the corner at the side end of the pressure contact surface 9e of the cancel cam 9 is brought into contact with the pressure surface 12a of the elastic contact material 12, as shown in FIG. 8.
Assuming that the rotating angle of the cancel cam 9 is xcex1, the angle formed by the pressure contact surface 9e and the line connecting the rotating shaft (upper shaft 9b) of the cancel cam 9 and the pressure surface 12a of the elastic contact material 12 is xcex2, the distance between the rotating shaft of the cancel cam 9 and the contact point is s, the pushing force from the elastic contact material 12 by the coil spring 11 is P, and the component force perpendicular to the line connecting the rotating shaft of the cancel cam 9 having a pushing force P and the contact point is W, component force W and moment T for returning the cancel cam 9 are expressed as follows:
W=Pxc3x97cos(xcex1+xcex2)
T=Wxc3x97s
Accordingly, it is considered to be a cause that since the angle (xcex1+xcex2) from the rotating shaft to the contact point is relatively large, value W decreases, thus not obtaining a sufficient moment.
If pressure force P is increased for measures against it, the size of the coil spring 11 is increased, making it difficult to arrange it in a narrow space between the cover 6 and the swing block 2.
Similarly, since the elastic contact material 12 must be decreased in length in the limited space on the swing block 2, the inclination of the elastic contact material 12 tends to increase, thus making it impossible to slide on the guide smoothly.
Accordingly, in consideration of the above problems, it is an object of the present invention to provide a canceling structure of a combination switch in which a sufficient moment is ensured to return the cancel cam, and a smooth motion of the elastic contact is provided without increasing the size of the spring.
To this end, according to an aspect of the invention, there is provided a canceling structure of a combination switch constructed such that a swing block for supporting a control lever is rotatably held on a fixing side; when the control lever is rotated from a neutral position, a cancel cam moves into the path of a cancel pin with the rotation of the swing block; and the cancel cam biases the swing block with the movement of the cancel pin in the opposite direction from the operating direction of the control lever, thereby returning the control lever to the neutral position, wherein the cancel cam comprises a shaft to be guided by a long hole provided on the fixing side in parallel with the direction to move into the path of the cancel pin; pressure contact surfaces are provided at positions on the peripheral surface of the shaft, closer to a steering shaft than to the control lever; when the cancel pin moves in the same direction as the operating direction of the control lever, the end thereof is pushed by the cancel pin, and allowed to rotate around the shaft; an elastic contact material having pressure surfaces that can be brought into contact with the pressure contact surfaces of the cancel cam is biased along a guide in the moving direction of the cancel cam; when the cancel cam rotates, the side end of the pressure contact surface is pushed by the pressure surface of the elastic contact material; and when released from the cancel pin, the cancel cam returns to a position before rotation by the pressure from the elastic contact material.
Since the pressure contact surfaces of the cancel cam pass through almost the center of the shaft, the component force in the direction of returning rotation by the pressure of the elastic contact material increases as compared with the case of being apart from the shaft.
According to another aspect of the invention, the shaft of the cancel cam expands from the pressure contact surfaces toward the elastic contact material and the pressure surfaces of the elastic contact material have a recessed portion for escaping the extension portion of the shaft.
Even when the shaft expands, the pressure surfaces of the elastic contact material can be brought into contact with the pressure contact surfaces of the cancel cam, thus increasing the length of the elastic contact material by the length that the pressure surfaces are extended to the pressure contact surfaces.